Hydrocephalus, a build-up of cerebrospinal fluid (CSF) in the intracranial space, is a disease that can cause significant neurological injury. Although the associated life-threatening intracranial hypertension can be well treated by diversion of cerebrospinal fluid to an absorptive surface outside of the brain, the short- and longterm cognitive effects of elevated intracranial pressure and altered cerebrospinal fluid pressure dynamics are incompletely understood. The overall objective of this proposal is to determine the cognitive effects of changes in intracranial pressure and altered CSF pressure dynamics in a population of hydrocephalics. In addition, these studies may help to determine the pressures needed to optimize cognitive outcome in the treatment of hydrocephalus. Specifically, the aims of the proposal are: (1) to determine the acute changes in cognitive function associated with graded increases in ICP seen after manipulations of novel programmable CSF shunting valves; (2) to determine the changes in cognitive function caused by the lowering of intracranial pressure (ICP) at the time of treatment of malfunctioning shunts; (3) to determine the cognitive deficits and post-treatment improvement in the sub-population of hydrocephalics with aqueductal stenosis who are treated by an internal CSF bypass procedure; and (4) to determine the shunting pressure dynamic that optimizes cognitive function when comparing the two most commonly used shunting valve systems: those that siphon and those that do not. We propose enrolling hydrocephalic patients as subjects for a series of studies addressing the above specific aims. Cerebrospinal fluid pressure dynamics will be measured using telemonitoring technology for the non-invasive measurement of ICP which is implanted in-line in the CSF shunting system as part of the standard clinical care of the hydrocephalic patient. Treatment outcome determination will be based on specific neuropsychological tests of higher cortical function. With this approach in the hydrocephalus model, we will be able to examine the effects of ICP changes on neurocognition, presumably determining which cognitive functions are ICP "sensitive" or ICP "resistant". At the study conclusion, derived data should also practically affect the surgical choice of shunting products.